Abstract
Leaf yellowing seriously affects the sustainability of artificial forest ecosystems. However, it remains unclear whether such chlorosis is driven primarily by soil nutrient deficiency or by internal nutrient reallocation. In particular, the physiological processes underlying the green apices and yellow bases pattern within branches remain poorly understood. This study compared needle carbon (C), nitrogen (N), and phosphorus (P) stoichiometry between apical and basal positions in asymptomatic and symptomatic Pinus sylvestris L. trees within the Otindag Sandy Land, China. Our findings revealed that except for the 80-100 cm layer, soil element concentrations did not differ significantly between healthy and chlorotic trees. In the trees, apical needles maintained stable stoichiometry across all trees, whereas basal needles of symptomatic individuals exhibited significantly higher C:N and C:P ratios, indicating severe localized nutrient stress. Notably, symptomatic trees exhibited exceptionally high N and P resorption efficiencies (79.68% and 71.05%, respectively), which were significantly higher than those of healthy trees (41.73% and 48.09%). The high Stoichiometric Deviation Index (SDI) and weak needle-soil correlations further confirm that needle chlorosis is decoupled from direct soil supply limitations. Instead, this pattern is primarily governed by prioritized internal nutrient reallocation to safeguard apical growth dominance. These findings highlight branch-level nutrient redistribution as a useful adaptive strategy to consider when interpreting early decline symptoms and nutrient stress in sandy-land P. sylvestris plantations.